The major cell surface glycoprotein fibronectin is usually decreased on tumor cells and is involved in cell adhesion. We have determined the functional organization of human plasma fibronectin. Protease-resistant domains for the binding of fibronectin to the plasma membrane, collagen, heparin, fibrin, actin, and DNA were mapped. The A and B subunits of human fibronectin were found to be similar but not identical in structural organization. Fibronectin was compared to the epithelial adhesive protein laminin. Laminin had equal hemagglutination activity, but much less activity in other assays for adhesion and effects on transformed cells. A cell mutant lacking gangliosides was defective in fibronectin distribution. Reconstitution of gangliosides restored a normal distribution, suggesting some role in fibronectin-membrane association. Recombinant DNA clones spanning the entire fibronectin gene were isolated and partially characterized. The gene was found to be unusually large and complex, with at least 48 exons of similar size. It may have evolved by gene duplication of primordial gene(s) 150 base pairs in size. New transformation-sensitive proteins of plasma membranes were identified by two-dimensional gel electrophoresis of membranes from cells transformed by wild-type and temperature-sensitive viruses. In collaborative studies, both fibronectin and high cell density were found to be necessary for rapid migration of embryonic neural crest cells, and the insulin receptor was further characterized. Our future objectives will be to evaluate the function of fibronectin using synthetic hybrids between different isolated domains, and by continuing structural and functional comparisons of the cellular and 2 plasma forms of fibronectin. Immunological approaches will be extended to characterize further the membrane components interacting with fibronectin and with insulin. The fibronectin gene will be characterized further in terms of structure.